1. Field of the Invention
This invention relates to the recycling of scrap material containing metallic aluminum or aluminum alloy contaminated with organic materials, such as paper, plastics, paint, lacquer, etc.
2. Description of the Prior Art
The recycling of process or post-consumer aluminum scrap materials is carried out on a large scale nowadays both for environmental and economic reasons. This is particularly true of such products as used beverage cans, metal turnings from manufacturing plants, recycled household waste, used aluminum foil, foil packaging materials, and the like. Known recycling processes involve melting the metal component of the waste material so that it can be recast into useful products. Before this can be done, however, it is usually necessary to remove contaminating organic materials, such as paper, plastics, lacquer, paints, oils and the like, in order to avoid contamination and oxidation of the molten metal by such materials or difficulties during the melting process. This decontamination process is usually referred to as "decoating" and is conventionally carried out as a separate step before the decoated metal is melted and processed further.
An example of a known decoating process is disclosed in International patent application Serial No. PCT/CA91/00252 published under publication number WO 92/01825 on Feb. 6, 1992 and assigned to the same assignee as the present application. The procedure disclosed in this application involves the introduction of the metal scrap into a fluidized bed of small particles at a temperature below the melting point of the metal in the presence of an oxidizing gas. An antioxidant material is introduced into the bed to prevent undue oxidation of the metal itself. The decoated metal is withdrawn from the fluidized bed after a suitable time to ensure completion of the decoating process, usually 3 to 15 minutes (more preferably 5 to 6 minutes), and is then subjected to a melting operation in a different apparatus and then to further recycling.
While this process is very effective for decoating many types of contaminated metals, it does not always work as effectively as might be desired with certain other materials, e.g. metal foils. Such foils are of very thin gauge, so the surface area is high and undue oxidation may take place during the decoating operation, thus reducing metal yields. Furthermore, the lightness of such scrap material means that the foil is easily disturbed by air currents and is thus difficult to handle in conventional types of decoating operations.
While the above disadvantages are most apparent when treating metal foil scraps, traditional decoating operations normally result in some metal loss when treating metal scraps of all kinds and usually require large capital outlays for the decoating equipment.
There is therefore a need for an improved procedure for decoating aluminum scraps of all kinds, and especially aluminum foil scraps.